Asymptotic power of likelihood-ratio tests for detecting quantitative trait loci using the COGA data

We investigated the asymptotic power of the likelihood-ratio test for detecting linkage to a quantitative trait locus (QTL) using the data set from the Collaborative Study on the Genetics of Alcoholism (COGA). Assuming a total trait heritability of 50% as determined for the COGA Cz P300 phenotype, we determined the minimum QTL heritability required at each point in the genome to achieve 80% power to detect linkage with a lod of 3.0. We find that there are regions of the genome where it is not possible to detect a QTL of any effect with 80% power, and that the overall minimum detectable QTL heritability for the COGA data is 0.35-0.40.